Phantom telephone circuit



Jan. 17, 1933. K. ZINN 1 ,894,335

PHANTOM TELEPHONE CIRCUIT Filed June 16, 1931 Y INVENTOR 1 5 .ZZEZznn BYW ATTORNEY Patented Jan. 17, 1933 UNITED STATES PATENT oFFrcsr t iMANVEL K. ZINN, or BROOKLYN, NEW Yonx, Ass'IGNoa- T AMERICAN TELEPHONEAND TELEGRAPH COMPANY, A CORPORATION or NEW YORK "PHANTOM TELEPHONEoimcur'r Application filed June 16, 1931. Serial No. 544,869.

- An object of myv invention is to provide apparatus and a correspondingmethod for reducing impedance irregularities in transmission circuits.Another object of my invention is to combine certain added reactanceswith a necessary reactance in a transmission line so as to form a"network whose impedance will be equal to the characteristic impedanceofthe line. Still another object of my invention is to provide addedreactance elements to form a network that shall obviate the impedanceirregularity in a phantom circuit due to leakage inductance in theloading coils of the side circuits. All these objects of my inventionand other objects and advantages will become apparent on considerationofthe specific example of practicein accordance with the invention which Idisclosein this specification. It will be understood that thisdisclosure relates principally to this particular example of theinvention, and 'that the scope of the invention will be'indicated in theappended claims. I 7

Referring to the drawing, Figure 1 is a diagrammatic cross-section of amulti-conductor cable built'up of spiral-8 units; Fig. 2 is adiagrammatic cross-section in more detail of one spiral-8 unit; Fig. 3is a circuit diagram showing the circuits and certain associatedelements of ap aratus for one spiral-8 unit in the cable Fig. 4 is asimplified diagram of a certain type of lattice network; and Fig. 5 is adiagram showing practical means for making compensation and adjustmentaccording tomy invention.-

The cable having the sheath 11 consists of coaxial layers 12 ofmulti-conductor units 13. All these units 13 in one layer 12 aredisposed inright-hand helical formation, as indicated by the arrow 14,but the units of the adjacent concentric shells are disposed inleft-hand helices, as indicated by arrow 15. Thus proceeding along aradius of the cable, the successive layers are disposed alternately inright and left-hand helices. In this way the crosstalk between onelayer, and another layer is minimized.

Each spiral-8 unit 13 consists of four twisted pairs 16, these pairsbeing twisted together to form a spiral-8. The two conductors 17 of asingle pair 16 forma side circuit which may be used for ordinarytelephone purposes. In Fig. 2 each solid black bar 18 joining theconductors 17 indicates symbolically such a side circuit. Two oppositepairs of side circuits in thespiral-S. are combined to form a phantomcircuit-r Thus in each spiral-8 there are four side circuits and twophantom circuits. These two phantom circuits are indicated in Fig. 2 bythe open or light face bars 19. 7 The diagram of Fig. 3 may be referredto as a kind of developed side elevationof Fig. 2. A single side circuitmay be seen extending from the terminal pair 20 to the terminal pair 21with repeating coils interposed as at 29. In the usual way, taps aretaken from the midpoints of the windings of the repeating coils 29, andthus from the conductor terminals 22 at one end a phantom circuit maybetraced to the conductor terminals 23 at the other end.

The side circuits such as 2021 have loading coils 2 1 at regularintervals. The normalmagnetic circuit for the loading coil 24 isindicated by the heavy line 25 in Fig. 3. For normal side circuitcurrents the windings of each coilare series aiding in the production ofmagnetic flux around the magnetic circuit 25. forces due to the twowindings on one. core buck each other for phantom circuit current andaccordin ly there will be some leakage flux, so that't ere will be linesof force such as 26 that will link with one of the windings of the coil24 but not with the other.

For convenience of explanation, switches are shown as at 27; let it beassumed that these switches are all opened. Under these circumstancesthe leakage flux for the phantom'circuit currents indicated by thedotted lines 26, will correspond to a degree of effective loading in thephantom circuit 22-23. A littlev loading inv this phantom circuit mightnot be objectionable if it were correctly proportioned. But theinductive reactance due to the leakage flux is a residual quantity andwill be quite variable. .The side circuit loading coils can be pairedwith respect to their. leakage inductances in the phantom circuit so asto insure longitudinal But the magnetomotive balance; but the inductancein the phantom circuit will then vary from one loading point to another,This irregularity will result in impedance irregularities which willincrease in this arrangement may be explained with reference to Fig. 4.

;Suppose 18a and 180 are the two conductors of a long transmission linewhich is normally of characteristic impedance R, but that in eachconductor there is interposed a coil 26 "of inductance value L. If theswitches 30 are open, the 'inductances L will cause refiection ofcurrent waves traveling along this-line.

By making lattice cross-connections through the condensers 28 andswitches 30, as shown in Fig. 4, and givin the condensers the propercapacity values the impedance looking into the network from one side canbe made equal to R, provided the network is terminated on the other sideby the impedance R, as is approximately the case for a long line. ty iscorrected and the lattice network comprising the inductances L andcapacities G acts only as a phase shifter, aside from a slight loss dueto the necessary resistance in the windings of the'coils. The capacity Cmust be such that'the formula R=-/' will be satisfied. Asexplained'above L will have different values from one loading point toanotherand accordingly C will have corresponding different values.

We may consider that 18a in Fig. 4: represents the phantom conductorformed by the pair 18a in Fig. 3, and similarly 180" represents theother conductor of the same phantom which is formed by the pair 180. Lor 26' represents theleakage inductance indicated in Fig. 3 by thedotted lines 26. 28 or C, in Fig. 4, represents the capacity between thetwo conductors of the phantom circuit that is afforded in Fig. 3 by thefour equal condensers 28'. It will be seen that between the two sides ofthe pair 18a and the two sides of the pair 180, in Fig. 3, there arefour possible cross-connections and accordingly there are four equalcondensers 28, one in each of these cross-connections, and eachproviding one-quarter of the eiiective capacity represented by C in Fig.4.

A jpractical procedure forgetting the desired capacities 28 is indicatedin Fig. 5 where two short lengths of ordinary quads 40 and 41 areprovided as stubs. The ends Thus the impedance irregulariof the eightconductors of these two quads are connected to the four conductors ofthe phantom circuit at the sides of the loading coil windings, as shownin Fig. 5. For

phantom circuit currents there will be no.

electromotive force across the conductors of a single pair in Fig. 5,but there will be an electromotive force across from pair to pair of thesamequad, and it will be seen that the capacity effect due to this lastmentioned elec tromotive force" gives the diagonal cross-capacitiescorresponding to the Us of Fig.4.

For side circuit currents, the twisted stub pairs will give capacity,but this will be no c more than for an equal lengthof line conductorpair and hence willbejrelatively in significant. If the quads areinconveniently long, convenient lengths can be assembled in parallel, asby using a section'of stub cable as many quads therein as found desir ae. a

phantom circuit reactance due to the leakage inductance of the coils,"analternative procedure is to neutralize only a part of such inductancereactance so as to equalize thereactance at all loading points. To thisextent the phantom circuit becomes a lightly loaded line, but it avoidsthe serious disad vantage of being. irregularly loaded, and thusinvolves no reflection efi'ects due to impedance irregularities.

Iclaim: i T

l 1. In combination, twoloaded side circuits and a phantom circuit, andmeans associated with the loading coils to neutralize their'leakageinductancereactance in the phantom c-ircuit. 2; In combination, acircuit having an outgoing conductor and a return conductor, aninductance coil having series aiding windings in said conductors, andmeans to neutralize the leakage inductance reactance of said windingswhen the said conductors are utilized in parallel. Y

I 3. Incombination, a circuit having an outgoing conductor and a returnconductor, an efiective' reactance element in said circuit in balancedrelation with respect to said conductors, said element beingineii'ective except for a small residual effect when the conductors areutilized in parallel, and means associated therewith to neutralize saidresidual efiect.

4. In combination, two loaded side circuits and a phantom circuit, andcondensers associated with the" loading coilsto neutralize their.leakage inductance reactance in the" phantom circuit. 3Q

5. In combination, two loaded side circuits and a phantomcircuit,lattice cross-connections at each loading coil from eachconductor of oneside'circuit to each conductor. of the ether side'circuit, andcondensers in these connections to neutralize the leakage induc- Insteadof completely neutralizing all the i tance reactance of the loadingcoils in the phantom circuit.

6. In combination, two loadedside circuits and a phantom circuit,lattice cross-connections at each loading coil from each conductor ofone side circuit to each conductor of the other side circuit, andreactance elements in these connections to neutralize the leakageinductance reactance of the loading coils in'the phantom circuit.

7 In combination, two loaded side circuits and a phantom circuit, and ateach loading coil means connecting across from one side circuit to theother to neutralize the leakage inductance reactances of thecoils in thephantom circuit.

8. In combination, two loaded side circuits and a phantom circuit, andcondensers at the loading coils connected in lattice arrangement fromthe conductors of each side circuit to the conductors of the other sidesubject to the formula R '/L/0 where R is the characteristic impedanceof the phantom circuit line, L is the leakage inductance of a loadingcoil in the phantom circuit and C is the capacity in one ofthe latticecross connections from one side circuit to the other. i

9. A cable comprising spiral-8 units, each such unit consisting of fourtwisted pairs, the opposite pairs being utilized for two phantomcircuits, loading coils in the four side circuitsof each spiral-8 unit,at each loading coil station, lattice connected condensers between thepairs of each phantom circuit to neutralize the leakage inductancereactance of the coils in the phantom circuits.

10. In combination, two loaded side circuits and a phantom circuit, theloading coils of the side circuits having unequal leakage inductancereactance in the phantom circuit from point to point, and means toneutralize a art of such reactance at each loading point so as toequalize the reactance at all the loading points. 7

11. In combination a circuit having an outgoing conductor and a returnconductor, and effective reactance elements in said circuit each inbalanced relation with respect to said conductors, and means to equalizethe efiec-t of said elements when the said conductors are utilized inparallel.

12. The method of neutralizing the leakage irregularities due to unequalleakage inductances of the side circuit loading coals in a phantomcircuit which consists in neutralizing a part of the correspondingreactance circuit,

June, 1931. I v

, MANVEL K. ZINN.

